The events of 11 September marked a turning point in US-Russian relations.

Faced with a new international terror threat, old Cold War rivalries were set aside, and a relationship beset for many years by mutual suspicion and open mistrust rapidly entered a completely new phase.

In Washington and at the Kremlin, the talk is of an "amenable relationship" and of "a genuine partnership less burdened by Cold War legacies".

According to one senior US official, the upcoming summit "really puts the Russian-US relationship on a firm course of long-term partnership, even a long-term alliance".

Since 11 September, the previously unthinkable has become a geopolitical reality.

The Russians have acquiesced in the American use of military bases in former Soviet republics, such as Kyrgyzstan, Tajikistan, and Uzbekistan.

Similarly, the presence of US military trainers in Georgia would once have been bitterly resisted in the Kremlin.

After the attacks on New York, Washington and Pennsylvania, Russia has provided the Americans with intelligence information and readily agreed to supply arms to the Northern Alliance in Afghanistan.

Putin's moment

With typical cunning and alacrity, President Vladimir Putin has seized his moment. It is an opportunity to forge a new relationship with the United States, winning greater acceptance for Russia's integration with the West and thus maintaining the country's wobbly position as a front-tier nation.

It was for good reason, then, that he rushed to become the first international leader to offer President Bush his condolences on 11 September.

Without question, the partnership is asymmetrical, because Russia is in no position to challenge America's global hegemony. But it is a partnership, nonetheless.

The US and Russia have agreed to 'virtual cuts' in their nuclear arsenals

Previous meetings between the two leaders, in Slovenia and Texas, have focused on developing a strong personal chemistry. This summit in Moscow and St Petersburg deals much more with substance.

Most importantly of all, Russia and America will sign a new arms reduction treaty, slashing their nuclear weapons by two-thirds.

Unlike previous accords, which took years to negotiate and hundreds of pages to codify, this is a flimsy three-page affair, which gives America enormous latitude.

Rather than dismantle many of its weapons, the Pentagon will be able to stockpile them.

This "virtual cuts" arms treaty has been rightly perceived as a major victory for Washington.

For Russia, meanwhile, it marks the abandonment of nuclear parity with the United States - a last symbol of its former superpower status.

Russia and Nato

Ahead of the summit, the two leaders have also agreed to a new relationship between Russia and Nato.

Indeed, after the Russian leg of the trip is over, Bush and Putin will be reunited in Rome for a Nato-Russian summit.

Under the terms of the landmark agreement reached last week in Iceland, Russia and Nato will set policy on a fixed range of issues, including counter-terrorism, the proliferation of nuclear weapons, missile defence, peacekeeping and civil defence.

Moscow will not have a veto over Nato decisions or influence the alliance's core defence role. But this still marks a major shift.

It will quiet Moscow's long-held opposition to an expanded Nato, which encompasses many of the Soviet Union's former satellites.

Russia has already softened its criticisms of America's plans to build a national missile defence system - largely in recompense for the arms cuts negotiated with Washington.

Putin is also looking for America to help facilitate Russia's rapid accession to the World Trade Organisation.

New 'strategic framework'

Points of divergence still exist. America is concerned about proliferation issues, namely the transfer of Russian nuclear and weapons technology to Iran, one of the countries included by President Bush as part of the "axis of evil".

Mr Bush hopes to convince Mr Putin to produce more energy

A particular sticking point is last year's $300m-a-year arms deal signed between Moscow and Tehran, making Iran the third biggest customer of Russian weapons, after China and India.

There are worries, too, about the safety of Russia's ageing nuclear arsenal and stockpiles of biological and chemical weapons.

And Mr Bush will use this opportunity to call for Russia to increase its energy sales in the world market.

In Moscow, Mr Bush and Mr Putin will lay out a new "strategic framework" to curb weapons proliferation and international terrorism and to stress closer economic relations and cultural exchanges.

President Bush says he is determined to "liquidate the legacy of the Cold War". In Mr Putin, he has a man he can do business with.